In the 1960s, Blakiston appeared in three episodes of The Avengers as well a number of ITC productions such as The Saint and the 1969 Randall and Hopkirk (Deceased) episode "Never Trust a Ghost". She appeared to great acclaim as Marjorie Ferrar in the BBC Television adaptation of Galsworthy's The Forsyte Saga in 1967. In 1977 she appeared in Raffles as Lady Paulton, and also in Murder Most English as Helen Carobleat.

In 1970, Blakiston married the actor Russell Hunter after they had played together in A Midsummer Night's Dream at the Open Air Theatre, Regent's Park. They had a son and a daughter together, but later divorced.

In 1983, Blakiston played the wayward character of Lady Patience Hardacre in the satirical Granada television series Brass, which ran for three series. She portrayed Mon Mothma, the primary political leader of the Rebel Alliance in the 1983 Star Wars film, Return of the Jedi.

In 1986, Blakiston played the villain Bess Sedgwick opposite Joan Hickson's Miss Marple, in the episode "At Bertram's Hotel" of the BBC's Miss Marple series. She also appeared as Lionel Hardcastle's ex-wife in an episode of As Time Goes By. She and Geoffrey Palmer (Lionel) had previously played estranged spouses a decade earlier in Carla Lane's series The Last Song. Since 2015, Blakiston has played Aunt Agatha in the BBC adaptation Poldark.